How to know whether an object is array or not?

 var x=[];

console.log(typeof x);//output:"object"
alert(x);//output:[object Object]
console.log(x.valueOf())//output:<blank>? what is the reason here?
console.log([].toString()); also outputs <blank>     
Object.prototype.toString.call(x) output:[object Array] how?

since console.log([].toString()); outputs :blank

1st:

why i get blank at 2nd last statement?

2nd:

Is there a way to know exactly what an object is: Array or plain Object({}) without the help of their respective methods like x.join() indicates x is an Array,not in this way.

Actually,in jquery selection like $("p") returns jquery object so if i use

console.log(typeof $("p"));//output:"object

I just wanted to know the actual Name of the Object.Thats it.Thank u for u help

javascript jquery
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